Sensor integrated circuit load current monitoring circuitry and associated methods

ABSTRACT

A sensor integrated circuit including a regulator for generating a regulated voltage includes a digital load configured to draw a load current from the regulator in response to a clock signal during in situ operation and a comparator configured to determine the absence or presence of a fault during in situ operation. The load current is less than or equal to a predetermined level in the absence of a fault and is greater than the predetermined level in the presence of a fault. The comparator is responsive to the load current and to a threshold level and is configured to generate a comparator output signal having a level indicative of whether the load current is less than or greater than the threshold level in order to thereby determine the absence or presence of a fault during in situ operation, respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD

This invention relates generally to fault testing of sensor integratedcircuits and more particularly to testing circuitry and methods for insitu fault testing.

BACKGROUND

Integrated Circuits (ICs) are used in a variety of sensing applications,many of which are have strict accuracy and reliability requirements dueto their use in safety critical applications such as automotiveapplications. One example application is in sensing applications inwhich a circuit including one or more sensing elements (e.g., pressuresensing elements, temperature sensing elements, light sensing elements,acoustic sensing elements, and magnetic field sensing elements) is usedto detect one or more parameters (e.g., pressure, temperature, light,sound, magnetic field). Magnetic field sensors, for example, arecircuits including one or more magnetic field sensing elements,generally in combination with other circuit components (e.g., analog,digital and/or mixed signal components), and are used to detect amagnetic field.

In high precision applications such as automobiles, accuracy in magneticfield sensing, such as may be used to detect motion of a target object,can be critical. Engine ignition timing, for example, depends onconsistent detection accuracy. As one example, when magnetic fieldsensing elements and/or other circuitry of a magnetic field sensorintegrated circuit (IC) in an engine ignition timing system are damageddue to overstress conditions, detection accuracy by the magnetic fieldsensor IC, and the resulting accuracy or performance of the engineignition timing system, can be negatively impacted. Furthermore, insafety critical applications such as automobiles, compliance withstandards such as Automotive Safety Integrity Level (ASIL) standards,generally requires safety mechanisms to ensure accurate and reliablecircuit operation.

As digital IC geometries become smaller and signal speeds become faster,fault testing becomes more challenging. Various fault conditions such asmarginal contacts, vias, and/or interconnects can cause signal delay andother types of faults. Testing of digital circuitry can be complicatedby the magnitude of logic gates and other circuitry and the resultingnumber of circuit nodes to be tested.

IC testing is often performed during manufacture, in a testingenvironment. Such testing includes exercising the circuitry in a mannerintended to emulate in situ conditions (i.e., conditions to which thesensor is expected to be exposed in actual use in a particularapplication and environment).

SUMMARY

According to the disclosure, a sensor integrated circuit including aregulator for generating a regulated voltage includes a digital loadconfigured to draw a load current from the regulator in response to aclock signal during in situ operation and a comparator configured todetermine the absence or presence of a fault during in situ operation.The load current is less than or equal to a predetermined level in theabsence of a fault and is greater than the predetermined level in thepresence of a fault. The comparator is responsive to the load currentand to a threshold level and is configured to generate a comparatoroutput signal having a level indicative of whether the load current isless than or greater than the threshold level in order to therebydetermine the absence or presence of a fault during in situ operation,respectively.

testing. In particular, faults arising from in situ conditions, such asfaults caused by application elements and parameters and/or caused bymanufacturing-related stresses (i.e., stresses due to IC installmentand/or use), can be detected. Additionally, the fault testing isaccomplished as a background function without adversely impactingcircuit operation.

Features may include one or more of the following individually or incombination with other features. The digital load can include aplurality of domains, each domain corresponding to a respectiveplurality of logic gates and controlled by a respective clock signal,wherein the sensor integrated circuit further comprises a controllerconfigured to generate the clock signal for each of the domains of thedigital load. The sensor IC may further include a threshold generatorconfigured to generate the threshold level, wherein the threshold levelis a based on the number of domains comprising the digital load.

least one of the clock signals can corresponds to a high activity clockassociated with a high sensor activity interval, at least one of theclock signals can correspond to a low activity clock associated with alow sensor activity interval, at least one of the clock signals cancomprise both a high activity clock portion associated with a highsensor activity interval and a low activity clock portion associatedwith a low sensor activity interval, at least one of the clock signalscan be periodic and/or at least one of the clock signals can benon-periodic.

The sensor IC may further include a latch responsive to the comparatoroutput signal and configured to latch the comparator output signal at adetection time. The detection time can follow a low sensor activityinterval. The detection time can substantially coincide with an edge ofa clock pulse following a low sensor activity interval. The detectiontime can substantially coincide with a falling edge of the clock pulsefollowing the low sensor activity interval.

Also described is a method of monitoring a digital load currentincluding detecting a load current drawn by an integrated circuitcomprising a plurality of digital load domains, during in situoperation, each digital load domain controlled by a respective clocksignal, wherein detecting the load current comprises comparing the loadcurrent to a threshold level to generate a comparison result andindicating the absence of a fault when the load current is less than thethreshold level and indicating the presence of a fault when the loadcurrent is greater than the threshold level.

Features may include one or more of the following individually or incombination with other features. Detecting the load current may furtherinclude enabling at least one first digital load domain controlled by aclock signal comprising a high activity clock interval, setting thethreshold level, and enabling at least one second digital load domaincontrolled by a clock signal comprising a low activity clock interval.The method may further include latching the comparison result at adetection time, which detection time may follow the low activity clockinterval. Indicating the absence or presence of a fault may includesampling the latched comparison result by a controller. Setting thethreshold level may include setting the threshold level based on thenumber of digital load domains.

DESCRIPTION OF THE DRAWINGS

The foregoing features may be more fully understood from the followingdescription of the drawings. The drawings aid in explaining andunderstanding the disclosed technology. Since it is often impractical orimpossible to illustrate and describe every possible embodiment, theprovided figures depict one or more illustrative embodiments.Accordingly, the figures are not intended to limit the scope of thebroad concepts, systems and techniques described herein. Like numbers inthe figures denote like elements.

FIG. 1 is a block diagram of a sensor IC including fault testingcircuitry for in situ fault testing according to the disclosure;

FIG. 2 is a block diagram of the load current monitoring circuitry ofthe sensor IC of FIG. 1;

FIG. 3 is a graph including several waveforms associated with the loadcurrent monitoring circuitry of FIG. 2 in the absence of a fault;

FIG. 3A is a graph including several waveforms associated with the loadcurrent monitoring circuitry of FIG. 2 in the presence of a fault; and

FIG. 4 is a flow diagram illustrating a process for in situ sensor ICfault testing based on load current monitoring.

DETAILED DESCRIPTION

Referring to FIG. 1, a sensor IC 10 includes load current monitoringcircuitry 20 according to the disclosure. The sensor IC 10 includes atleast one regulator for generating a regulated voltage based on a supplyvoltage, VCC. Here the IC 10 includes a first regulator 12 forgenerating a first regulated voltage 12 a, here a VREG_A voltage topower analog circuitry 30 and a second regulator 14 for generating asecond regulated voltage 14 a, here a VREG_D voltage to power digitalcircuitry and controller 40 (referred to alternatively as digital load40). Isolation circuitry 16 can be coupled between the analog regulator12 and the digital regulator 14 to prevent loading on the digital supplyVREG_D by monitoring circuitry 20.

As used herein, the terms “processor” and “controller” are used todescribe electronic circuitry that performs a function, an operation, ora sequence of operations. The function, operation, or sequence ofoperations can be hard coded into the electronic circuit or soft codedby way of instructions held in a memory device. The function, operation,or sequence of operations can be performed using digital values or usinganalog signals. In some embodiments, the processor or controller can beembodied in an application specific integrated circuit (ASIC), which canbe an analog ASIC or a digital ASIC, in a microprocessor with associatedprogram memory and/or in a discrete electronic circuit, which can beanalog or digital. A processor or controller can contain internalprocessors or modules that perform portions of the function, operation,or sequence of operations. Similarly, a module can contain internalprocessors or internal modules that perform portions of the function,operation, or sequence of operations of the module.

An oscillator 50 is configured to generate an oscillator output signal52 to control the digital circuitry and controller 40. Moreparticularly, the digital load 40 can include a plurality of domains,each corresponding to a respective plurality of logic gates andcontrolled by a respective clock signal. The controller 40 can beconfigured to generate a master, or system clock signal in response tothe oscillator output 52 and also to generate a plurality of domainclock signals based on the master clock signal. Output circuitry 60 canbe coupled to receive signals 42 from the digital circuitry andcontroller 40 and to generate one or more sensor IC output signals. Onesuch signal 42 from the controller 40 can include a fault detectionsignal (e.g., signal 42 a in FIG. 2).

In operation, the digital circuitry and controller 40 draws a loadcurrent I_(L) from the digital regulator 14 in response to one or moreclock signals during in situ operation. Testing in situ refers totesting of the sensor IC 10 in its intended application, as contrastedto testing in a manufacturing setting. The load current I_(L) is lessthan or equal to a predetermined level in the absence of a fault and isgreater than the predetermined level in the presence of a fault. As usedherein, the term “predetermined,” when referring to a value or signal,is used to refer to a value or signal that is set, or fixed, in thefactory at the time of manufacture, or by external means, e.g.,programming, thereafter. As used herein, the term “determined,” whenreferring to a value or signal, is used to refer to a value or signalthat is identified by a circuit during operation, after manufacture.

The monitoring circuitry 20 is coupled to the analog regulator 12, thedigital regulator 14, and the digital circuitry and controller 40 and isconfigured to monitor the load current to detect a fault. Moreparticularly, the monitoring circuitry 20 may include a comparator (FIG.2) responsive to the load current and to a threshold level or signal andgenerate a comparator output signal having a level indicative of whetherthe load current is less than or greater than the threshold level inorder to thereby determine the absence or presence of a fault during insitu operation.

The sensor IC 10 may take various forms. As examples, the IC 10 can be apressure sensor, an accelerometer, a flow sensor, or a magnetic fieldsensor for sensing one or more parameters of a target 18 based onvariations in a magnetic field. In the case of a magnetic field sensorIC, analog circuitry 30 may include one or more magnetic field sensingelements. Sensing elements can take a variety of forms, including, butnot limited to, a Hall effect element, a magnetoresistance element, or amagnetotransistor. As is known, there are different types of Hall effectelements, for example, a planar Hall element, a vertical Hall element,and a Circular Vertical Hall (CVH) element. As is also known, there aredifferent types of magnetoresistance elements, for example, asemiconductor magnetoresistance element such as Indium Antimonide(InSb), a giant magnetoresistance (GMR) element, for example, a spinvalve, an anisotropic magnetoresistance element (AMR), a tunnelingmagnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).The magnetic field sensing element may be a single element or,alternatively, may include two or more magnetic field sensing elementsarranged in various configurations, e.g., a half bridge or full(Wheatstone) bridge. Depending on the device type and other applicationrequirements, the magnetic field sensing element may be a device made ofa type IV semiconductor material such as Silicon (Si) or Germanium (Ge),or a type III-V semiconductor material like Gallium-Arsenide (GaAs) oran Indium compound, e.g., Indium-Antimonide (InSb). As used herein, theterm “magnetic field signal” is used to describe any signal that resultsfrom a magnetic field experienced by a magnetic field sensing element.

Example magnetic field sensor types can include a rotation detector, amovement detector, a current sensor, or a proximity detector. A rotationdetector can sense rotation of a target object 18, for example, advanceand retreat of magnetic domains of a ring magnet or advance and retreatof gear teeth of a ferromagnetic gear. Target 18 can have a variety offorms, including, but not limited to a gear having gear teeth or a ringmagnet having one or more pole pair. Also, linear arrangements offerromagnetic objects that move linearly are possible. The term“movement detector” can be used to describe either a rotation detectoror a magnetic field sensor that can sense different movement, e.g.,linear movement, of a ferromagnetic object, for example, linear movementof magnetic domains of a ring magnet or linear movement of gear teeth ofa ferromagnetic gear. A magnet can be placed at a variety of positionsproximate to the target 18, resulting in fluctuations of a magneticfield proximate to the gear as the gear rotates in a so-called“back-bias” arrangement.

Magnetic field sensors are used in a variety of applications, including,but not limited to an angle sensor that senses an angle of a directionof a magnetic field, a current sensor that senses a magnetic fieldgenerated by a current carried by a current-carrying conductor, amagnetic switch that senses the proximity of a ferromagnetic object, arotation detector (or movement detector) that senses passingferromagnetic articles, for example, magnetic domains of a ring magnetor a ferromagnetic target (e.g., gear teeth) where the magnetic fieldsensor is used in combination with a back-bias or other magnet, and amagnetic field sensor that senses a magnetic field density of a magneticfield.

Analog circuitry 30 may additionally include other circuitry such as afront-end amplifier to process the magnetic field sensing element outputsignal to generate a further signal for coupling to an analog-to-digitalconverter (ADC) as may include one or more filters, such as a low passfilter and/or notch filter, and as may take the form of a sigma deltamodulator to generate a digital magnetic field signal. The ADC maygenerate digital signals for coupling to and further processing bydigital circuitry and controller 40.

It will be appreciated that the circuits and techniques described hereinapply to any sensor type that contains digital circuitry 40 desired tobe monitored for one or more fault conditions. The fault detectiondescribed herein relies on a difference between the digital circuitryload current I_(L) in the presence of a fault and in the absence of afault. The load current I_(L) can be referred to as Iddq current toindicate a quiescent state current (i.e., when the digital circuitry isnot switching because clock inputs are held at static states).Alternatively, when the IC 10 is being exercised in normal use (i.e.,the digital circuitry is operating in response to dynamic clock signalinputs and is expected to draw a “shoot through” current at clocktransitions), the load current I_(L) can be referred to as Idd current.During normal operation in the intended application (i.e., in situoperation), it is not possible to turn off the clock signals and stillremain fully operational. Thus, according to the disclosure, faulttesting is performed while the digital domains receive their respectiveclock signals. However, in order to leverage fault detection by anexpected difference between Iddq and Idd currents, the present circuitsand techniques perform fault testing when the load current is as closeto Iddq current as possible, but without adversely affecting sensoroperation.

It will be appreciated that some digital domain clock signals haveperiods of inactivity or reduced activity as may be referred to as idleperiods. During these idle periods, there may be more sparse or sporadicclock edges than at other times. These types of clock signals can bereferred to as low activity clock signals and can be associated with alow sensor activity interval. High activity clock signals on the otherhand refer to clock signals associated with a high sensor activityinterval and generally do not have idle periods (or have very rare idleperiods). Some clock signals can include both a high activity clockportion associated with a high sensor activity interval and a lowactivity clock portion associated with a low sensor activity interval.Furthermore, clock signals can be periodic or non-periodic.

In the case of an example magnetic field sensor in the form of arotation detector, digital controller 40 processes signals 32 from theADC of the analog circuitry 30 to determine the speed and/or directionof movement, such as rotation of target 18 and outputs one or moredigital signals 42 to output circuit 60. More particularly, in thisexample sensor, controller 40 can determine the speed and/or directionof target 18 based on digital signals 32 and can combine thisinformation with fault information in some embodiments to generate thesensor output signal 62 in various formats. The output circuitry 60 canprovide the sensor output signal 62 in various formats, such as aso-called two-wire format in which the output signal is provided in theform of current pulses on the power connection to the sensor or athree-wire format in which the output signal is provided at a separatededicated output connection. Formats of the output signal 62 can includevariety of formats, for example a pulse-width modulated (PWM) signalformat, a Single Edge Nibble Transmission (SENT) format, a SerialPeripheral Interface (SPI) format, a Local Interconnect Network (LIN)format, a CAN (Controller Area Network) format, an Inter-IntegratedCircuit (I²C) format, or other similar signal formats.

In some applications, a system controller, such as an Engine ControlUnit (ECU) in the case of an automotive application (not shown), canrespond to fault information from the sensor 10 by commanding the sensorto operate in a certain manner in the presence of a fault. For example,in the presence of a major fault, the ECU may cause the sensor 10 toshut down; whereas, in the case of a minor fault, the ECU can cause thesensor to continue normal or modified operation.

Referring also to FIG. 2, a portion of the sensor IC 10 is shown toillustrate details of the load current monitoring circuitry 20. As notedabove, the load current monitoring circuitry 20 is coupled to the analogregulated voltage VREG_A 12 a and to the digital regulated voltageVREG_D 14 a. Transmission gates 13, 15 can be provided to enable loadcurrent monitoring in response to an enable signal 17 (e.g.,EN_ASIL_IDD_CHECK) from the controller. Closing transmission gate 13 cancause a predetermined resistance of resistor 19 to be provided betweenthe analog and digital regulated voltages 12 a, 14 a and closingtransmission gate 15 can couple the digital regulated voltage VREG_D 14a to the digital load 40 when it is desired to sample the load currentby current monitoring circuit 20. For example, load current monitoringcircuit 20 can sample the load current at a time when shoot throughcurrent to the digital load 40 has subsided (e.g., at the falling edgeof a clock signal).

As noted above, load current monitoring circuitry 20 includes comparator200 that is responsive to the load current I_(L) at an input 200 a andto a threshold level at an input 200 b and configured to generate acomparator output signal at an output 200 c having a level indicative ofwhether the load current is less than or greater than the thresholdlevel in order to thereby determine the absence or presence of a faultduring in situ operation, respectively. More particularly, anoperational amplifier 210 can be coupled to the digital regulatedvoltage to generate a signal A_IDD proportional to the load current(i.e., the sampled load current). Isolation circuitry 16 (and inparticular the right-most NMOS) ensures that the resistor loading ofoperational amplifier 210 does not load the VREG_D bus. The left-mostNMOS of isolation circuitry 16 ensures that the voltage drop on bothsides matches.

It should be understood that a so-called “comparator” can be comprisedof an analog comparator having a two-state output signal indicative ofan input signal being above or below a threshold level (or indicative ofone input signal being above or below another input signal). However,the comparator can also be comprised of a digital circuit having anoutput signal with at least two states indicative of an input signalbeing above or below a threshold level (or indicative of one inputsignal being above or below another input signal), respectively, or adigital value above or below a digital threshold value (or anotherdigital value), respectively.

A threshold generator 220 can be provided to generate one or morethreshold signals for comparison the A_IDD signal. In the exampleembodiment shown in FIG. 2, the threshold generator 220 is provided by aresistor divider 222 with selectable taps at intermediate nodes togenerate different threshold voltage levels in response to a controlsignal 224. In general, the variable threshold level establishes thepass/fail point of the sensor. Various schemes are possible forestablishing a threshold signal for comparison to the A_IDD signal. Insome embodiments, a user can provide the signal 224 to thereby selectthe threshold level. Alternatively, one or more fuses can be blown tostatically select a threshold level during manufacture of the sensor 10.As a further alternative, a state machine can be used to cycle throughvarious threshold levels in a round-robin fashion.

The threshold level may be selected to be a lower threshold (i.e., amore aggressive threshold level closer to the Iddq level) or may be ahigher level (i.e., a less aggressive threshold level closer to Idd thanto Iddq). For example, in some embodiments, the threshold level is basedon the number of concurrently active domains comprising the digitalload. In particular, a lower threshold level may be selected (i.e., amore aggressive threshold level closer to the Iddq level) when there arefewer concurrently active domains (i.e., fewer clock edges); whereas ahigher threshold level may be selected (i.e., a less aggressivethreshold level closer to Idd than to Iddq) when there are moreconcurrently active domains (i.e., more clock edges).

A flip-flop 230 can be coupled to receive the comparator output signalat a D input 230 a and generate a fault detection signal 42 a at a Qoutput 230 c (e.g., ASIL_PASS_FAIL_FLAG) for coupling to outputcircuitry 60 (FIG. 1). The flip-flop 230 can be clocked by a signal atits clock input 230 b generated by the controller 40 (FIG. 1). In theexample embodiment, a master clock signal 226 (MASTER_CLK) is invertedby inverter 232 and combined with a fault detection sample, or enablesignal 228 (ASIL_IDD_SAMPLE_ENABLE) through an AND gate 234, as shown.With this arrangement, the flip-flop 230 samples on the opposite phaseof the system or master clock signal 226 (i.e., at the falling edge ofthe master clock when shoot through current has subsided) and at timesestablished by the enable signal 228. In some embodiments, safetyspecifications such as ASIL dictate the frequency at which the A_IDDsignal is sampled.

Referring to FIG. 3, example waveforms associated with the sensor IC 10of FIGS. 1 and 2 are shown in the absence of a fault. The illustratedwaveforms include a master clock signal 300 (that can be the same as orsimilar to the master clock signal 226 of FIG. 2) as may be generated bythe controller 40 in response to the oscillator signal 52. Aninitialization clock signal 304 can be generated by the controller 40 inresponse to the master clock signal 300. Each of clock signals 310, 312,and 314 corresponds to a clock signal generated by the controller 40 andintended to control a respective domain of the digital load circuitry.Example clock signals include a temperature sensor check clock signal310 to control a temperature domain, an offset compensation check clocksignal 312 to control an offset compensation domain, and a gaincompensation check signal 314 to control a gain compensation domain.Clock signals 310, 312, and 314 are examples of clock signals havingboth high activity clock portions (e.g., as labeled 310 a for clocksignal 310) during which the clock signal is actively generating clockedges and low activity clock portions (e.g., as labeled 310 b for clocksignal 310) during which the clock signal is idle with fewer or no clockedges.

A fault IDD check clock signal 320 (that may be the same as or similarto the ASIL_IDD_SAMPLE_EN signal 228 of FIG. 2) controls the timing offault detection by the load current monitoring circuitry 20. Whenasserted, the fault IDD check clock signal 320 causes the load currentmonitoring circuitry 20 to test the load current to determine whetherthe load current is less than or greater than the threshold level inorder to thereby determine the absence or presence of a fault during insitu operation. The threshold level to which the comparator 200 (FIG. 2)compares the sampled load current signal 360 is labelled 330 and isreferred to alternatively as the load current check pass/fail threshold.The load current signal 360 can be the same as or similar to the sampledload current A_IDD in FIG. 2. It will be appreciated that although clocksignals 310, 312, and 314 have time coincident, or time simultaneousclock pulses (i.e., clock signals 310, 312, 314 can be described ashaving overlapping portions of high activity) other example clocksignals can have non-simultaneous clock pulses (i.e., clock signalscould alternatively have sequential high activity portions).

At a time labeled T1, a pulse on fault IDD check clock signal 320 causesthe comparator output signal 226 (FIG. 2) to be latched by flip-flop230, as occurs at a time labeled T2.

As shown, time T1 is as far from the interval of high clock activity aspossible in order to sample the load current when it is as close to Iddqas possible. Stated differently, the detection time established by thefault IDD check clock signal pulse at time T1 follows a low sensoractivity interval. It will be appreciated that for clock signals that donot have idle portions or portions of lower activity, it is not possibleto sample the load current any closer to Iddq than would occur on thefalling edges of the clock signal.

The condition of the load current signal 360 being below the threshold330 at sampled time T1 is indicative of the absence of a fault.

Referring also to FIG. 3A, the same example clock signals as shown inFIG. 3 are here shown under operating conditions associated with afault. More particularly, in FIG. 3A, at time T1 when a pulse on faultIDD check clock signal causes the comparator output signal 226 to belatched, a fault exists as is indicated by the condition of sampled loadcurrent signal 360 being above the threshold 330. The resulting faultindication can be a pass/fail indication without providing any furtherindication of which domain(s) is experiencing the fault or the systemcould have customized samples that would be triangulated to additionallyprovide an indication of which domain(s) experiences the fault.

Referring to FIG. 4, a flow diagram illustrates a method 400 ofmonitoring a digital load current during in situ operation. The methodbegins at block 402. In a block 404, a load current is sampled during insitu operation as may be initiated by an enable signal (e.g.,ASIL_IDD_SAMPLE_EN 228, FIG. 2) and as may include comparing the sampledload current to a threshold level to generate a comparison result. Thedetected load current can be load current I_(L) drawn by digitalcircuitry including a plurality of digital load domains, each domaincontrolled by a respective clock signal.

In embodiments, detecting the load current at block 404 can includeenabling at least one first digital load domain controlled by a clocksignal comprising a high activity clock interval, setting the thresholdlevel, and enabling at least one second digital load domain controlledby a clock signal comprising a low activity clock interval. Setting thethreshold level can include setting the threshold level based on thenumber of digital load domains. Detecting the load current at block 404can further include latching the comparison result at a detection time.For example, the detection time can follow the low activity clockinterval.

In block 408, the method includes indicating the absence of a fault whenthe load current is less than the threshold level and indicating thepresence of a fault when the load current is greater than the thresholdlevel. The fault indication can be provided to a system controller byoutput signal 42 a (e.g., signal ASIL_PASS_FAIL_FLAG of FIG. 2) andindicating the absence or presence of a fault at block 408 can includesampling the latched comparison result by a controller. The method endsat block 410.

It will be appreciated that the method 400 is a “background” operationperformed during normal in situ operation. In other words, the methoddoes not interrupt normal operation controlled by domain clock signals;rather, the method calls for sampling the load current (block 404) attimes of lower sensor activity where possible.

All references cited herein are hereby incorporated herein by referencein their entirety.

While electronic circuits shown in figures herein may be shown in theform of analog blocks or digital blocks, it will be understood that theanalog blocks can be replaced by digital blocks that perform the same orsimilar functions and the digital blocks can be replaced by analogblocks that perform the same or similar functions. Analog-to-digital ordigital-to-analog conversions may not be explicitly shown in the figuresbut should be understood.

Having described preferred embodiments, it will now become apparent toone of ordinary skill in the art that other embodiments incorporatingtheir concepts may be used. Elements of different embodiments describedherein may be combined to form other embodiments not specifically setforth above. Various elements, which are described in the context of asingle embodiment, may also be provided separately or in any suitablesubcombination. Other embodiments not specifically described herein arealso within the scope of the following claims.

It is felt therefore that these embodiments should not be limited todisclosed embodiments, but rather should be limited only by the spiritand scope of the appended claims.

What is claimed is:
 1. A sensor integrated circuit comprising aregulator for generating a regulated voltage based on a supply voltagecoupled to the sensor integrated circuit, comprising: a digital loadconfigured to draw a load current from the regulator in response to aclock signal during in situ operation, wherein the load current is lessthan or equal to a predetermined level in the absence of a fault andwherein the load current is greater than the predetermined level in thepresence of a fault; and a comparator responsive to the load current andto a threshold level and configured to generate a comparator outputsignal having a level indicative of whether the load current is lessthan or greater than the threshold level in order to thereby determinethe absence or presence of a fault during in situ operation,respectively.
 2. The sensor integrated circuit of claim 1, wherein thedigital load comprises a plurality of domains, each domain correspondingto a respective plurality of logic gates and controlled by a respectiveclock signal, wherein the sensor integrated circuit further comprises acontroller configured to generate the clock signal for each of thedomains of the digital load.
 3. The sensor integrated circuit of claim2, further comprising a threshold generator configured to generate thethreshold level, wherein the threshold level is a based on the number ofdomains comprising the digital load.
 4. The sensor integrated circuit ofclaim 2, wherein at least one of the clock signals corresponds to a highactivity clock associated with a high sensor activity interval.
 5. Thesensor integrated circuit of claim 2, wherein at least one of the clocksignals corresponds to a low activity clock associated with a low sensoractivity interval.
 6. The sensor integrated circuit of claim 2, whereinat least one of the clock signals comprises both a high activity clockportion associated with a high sensor activity interval and a lowactivity clock portion associated with a low sensor activity interval.7. The sensor integrated circuit of claim 2, wherein at least one of theclock signals is periodic.
 8. The sensor integrated circuit of claim 2,wherein at least one of the clock signals is non-periodic.
 9. The sensorintegrated circuit of claim 1, further comprising a flip-flop responsiveto the comparator output signal and configured to latch the comparatoroutput signal at a detection time.
 10. The sensor integrated circuit ofclaim 9, wherein the detection time follows a low sensor activityinterval.
 11. The sensor integrated circuit of claim 9, wherein thedetection time substantially coincides with an edge of a clock pulsefollowing a low sensor activity interval.
 12. The sensor integratedcircuit of claim 11, wherein the detection time substantially coincideswith a falling edge of the clock pulse following the low sensor activityinterval.
 13. A method of monitoring a digital load current comprising:detecting a load current drawn by an integrated circuit comprising aplurality of digital load domains, during in situ operation, eachdigital load domain controlled by a respective clock signal, whereindetecting the load current comprises comparing the load current to athreshold level to generate a comparison result; and indicating theabsence of a fault when the load current is less than the thresholdlevel and indicating the presence of a fault when the load current isgreater than the threshold level.
 14. The method of claim 13, whereindetecting the load current further comprises: enabling at least onefirst digital load domain controlled by a clock signal comprising a highactivity clock interval; setting the threshold level; and enabling atleast one second digital load domain controlled by a clock signalcomprising a low activity clock interval.
 15. The method of claim 14,further comprising latching the comparison result at a detection time.16. The method of claim 15, wherein the detection time follows the lowactivity clock interval.
 17. The method of claim 15, wherein indicatingthe absence or presence of a fault comprises sampling the latchedcomparison result by a controller.
 18. The method of claim 14, whereinsetting the threshold level comprises setting the threshold level basedon the number of digital load domains.